blower, bowler, nobler
The longest word you can make using those letters once is "keyboard."
There is no 8-letter anagram word. The letters can spell "ye stable" "easy belt" and "steel bay." The longest word is "beastly" (there may have been an extra E in the question).
Decade
you are rubbish arent you
The longest word starting with E is Electroencephalographically.
The longest word you can make with the letters a, b, c, d, e, f, x, y, and m is "decaf." It is a five-letter word that refers to coffee from which most of the caffeine has been removed. Other combinations yield shorter words, but "decaf" is the most extended valid option using these specific letters.
Treble is the word.
The longest is a four-letter word: dean
slobber
Kweebnf
Erectile
Abduce